* Compiler cleanup
This is general compiler cleanup, especially around the codegen part. Goals here were too:
1. Make it possible to compile HTML recursively (needed for future astro-in-expressions work) by moving that work into its own function.
1. Get rid of collectionItems and have compiling the HTML return just a source string.
Also not planned, this change gets rid of the different between components and pages. All Astro components compile to the same JavaScript.
* Remove unused node types
